1. Field of the Invention
The present invention generally relates to a thermal printer for printing labels and a method for printing labels therewith. Such labels can generally be, for example, labels for being applied to shelves for identifying the material present as would be used in warehouses, or labels including pricing information as would be used in grocery stores. Such labels may also have an adhesive backing for being applied to surfaces, or could be standard paper which could be fastened by other application means. More particularly, the present invention relates to apparatus for essentially automatically adjusting the print of a thermal printer during printing of such labels, and the method for adjusting the print. Thermal printers of the type utilized by the present invention generally have a few basic components as outlined below:
a) a thermal print head with a series of electrically controlled heating elements which are held in contact with a counterpressure roller, whereby a label strip to be printed on can be introduced between the heating elements and the counterpressure roller; PA1 b) devices to hold a payoff reel and a takeup reel for a thermal transfer ink ribbon which can be introduced by means of deflector rollers between the heating elements and the label strip, PA1 c) a control circuit connected to the thermal print head to control the thermal printer, and PA1 d) a computer processor connected to the control circuit.
2. Background Information
Such thermal printers as broadly described above are widely known. Typically, the thermal print heads used in such thermal printers are designed so that they can print directly on labels consisting of temperature-sensitive paper, and also on labels consisting of conventional paper, wherein, for the latter, a thermal transfer ink ribbon coated with temperature-sensitive ink must also be used.
It is generally known that direct printing on temperature-sensitive paper requires more thermal energy to activate the thermal print head than when printing with thermal transfer ink ribbon. For this reason, when the label material, and thus the printing method are changed, the control circuit of the thermal print head must also be adjusted in accordance with the modified printing conditions. In addition, there are also a large number of different types of thermo-paper, or thermo-labels, which are characterized by a paper-specific temperature sensitivity. For each of these different materials, a good quality printed image can only be successfully achieved if the thermal print head has reached a specified temperature.
In the above-discussed situations, if insufficient thermal energy is applied to the print head, the temperature-sensitive label paper will not be sufficiently darkened, and the image can appear on the label in varying shades of grey. If, on the other hand, the thermal energy applied during printing is too great, the thermal print head will be unable to cool down rapidly to the temperature at which the thermal paper is no longer discolored, so that parts of the paper which are not to be printed can also be discolored when they come into contact with the thermal print head, thus "smearing" the image. In the past, the adaptation of the thermal print head control to the type of paper used has essentially been done manually, and essentially has to be repeated every time the paper is changed. Further, each adjustment of the print head control can generally require several time-consuming tests and adjustments, until the image produced by the thermal printer on the labels is of an appropriate print quality.
On known thermal printers as discussed above, after the adjustment of the thermal print head control for the type of paper being used, no consideration is typically given to the fact that the thermal print head can assume different temperatures. It has been determined that, with higher temperatures of the print head, possibly due to climatic temperature fluctuations or to the heat generated by the thermal printer itself, etc., less thermal energy can be used to activate the thermal paper. Such temperature fluctuations can therefore significantly reduce the print quality of the thermal printer as excess heat could be generated thereby "smearing" the image.